The present invention relates generally to respiratory protective devices and more particularly, to an exhaled air pressured hood enclosure.
Respiratory protective hoods benefit from positive air pressure within the hood to keep out contaminated, ambient air. This plenum provides a substantial level of protection should the protective enclosure be temporarily compromised. A significant danger exists when wearers of respiratory hoods breathe in air within the hood that may introduce harmful contaminants into the hood. One solution to this problem is to utilize exhaled air to keep the hood inflated and pressurized thereby creating a plenum against the introduction of ambient air. However, with each breath of exhaled air, the wearer introduces additional carbon dioxide and humidity into the hood.
The air that enters the lungs contains approximately 21 percent oxygen and 0.04 percent carbon dioxide. By contrast, the air that leaves the lungs contains 14 percent oxygen and 4.40 percent carbon dioxide. Consequently, a high level of carbon dioxide may accumulate within the hood.
Humidity is a measure of the amount of water vapor in the air. The air""s capacity to hold vapor is limited but increases dramatically as the air warms, roughly doubling for each temperature increase of 10xc2x0 C. (18xc2x0 F.). As the body is exhaling warm, moist air, the humidity within the hood becomes increasingly high. In combination with a high concentration of carbon dioxide, this results in the hood becoming uncomfortably hot. In addition, outward vision while wearing a protective hood is typically achieved through the use of a transparent material integrated into the hood in front of the eyes. By accumulating carbon dioxide and humidity within the hood, moisture accumulates on the transparent material thereby inhibiting outward vision.
Another drawback in the prior art is that even if the user properly exhales into the hood to create the plenum, air pressure may reduce over time that requires the user to continually monitor the plenum in the hood to be assured that sufficient positive air pressure exists.
Standard gas masks must be manufactured in many different sizes because the structure of the nose and mouth area varies widely in populations including children and adults. It is logistically impractical for an authority responding to an emergency involving a large population to transport and fit a conventional face sealing gas mask to the victims. Face sealing gas masks must accommodate the variations of individual faces which would require the responding authority to not only stock and transport an inordinate number of masks, but it would also requires the authority to take a significant amount of time to assign the correct mask to the individual. Further compounding this problem is the fact that conventional face sealing gas masks must be adjusted to the fit the wearer. Again, this consumes a significant amount of time that may not be available, particularly when a large number of victims need assistance at the same time. What is needed is a protective device that can be quickly donned, yet accommodate the varying physiological differences within a given population.
Hooded masks are generally secured around the circumference of the neck and benefit from enhanced protection of the head area. However, this circumference can vary widely in a population. Furthermore, belts, elastic bands and the like are often used to tighten the seal between the hood and the neck. This tightening is difficult and time-consuming to achieve in an emergency situation and the user may either make the seal too loose and not provide adequate protection or may make the seal too tight leading to an uncomfortable fit that presses against the arteries and veins in the neck.
Another problem in the prior art involves the speed of donning the protective hood and establishing a secure respiratory pathway. Some hood embodiments in the prior art require the user to exhale into the hood before engaging the air filtration system. This added step not only adds to the time in which the hood becomes effective, but also increases the level of training needed to operate the hood properly. In many applications, protective hoods are designed for use in high-stress, dangerous environments. Reducing the speed in which the hood becomes effective and reducing the training required for operating the hood is beneficial. Furthermore, protective hoods may be distributed to an untrained civilian population that may have little or no training in donning and operating the protective hoods correctly. Therefore, simplification of operation and speed of use again become advantageous.
An object of this invention is to provide an air purifying respirator hood that automatically creates a plenum around the head.
Another object of this invention is to reduce the amount of moisture and carbon dioxide within the ocular region of a hood inflated by the wearer""s exhalation.
Another object of this invention is to increase the overall protection factor of an air purifying respirator hood by establishing one or more pressurized zones against the introduction of ambient air into the hood enclosure.
Another object of this invention is to provide a continuously pressurized hood without the need for an external air source.
Another object of this invention is to provide a protective respirator hood having a substantially universal fit.
Previous attempts have been made to provide a protective hood enclosure such as described in U.S. Pat. No. 5,495,847 to Hu (""847 patent); U.S. Pat. No. 5,411,017 to Wong (""017 patent); U.S. Pat. No. 4,870,959 to Reisman et al. (""959 patent); U.S. Pat. No. 5,186,165 to Swann (""165 patent); U.S. Pat. Nos. 3,935,861 and 3,680,555 to Warncke (""861 and ""555 patents); all of which are incorporate herein by reference.
The ""017 patent to Wong describes a protective enclosure having elastic collars on the top and bottom. The bottom collar is closed against the wearer""s neck and the top collar is closed against the wearer""s head. Once donned, ambient air trapped within the protective enclosure is breathed in providing three to five minutes of escape time. However, exhaled air is trapped within the protective enclosure thereby accumulating moisture and carbon dioxide within the enclosure.
The ""847 patent to Hu describes a survival hood comprising a hood for the head and neck which has an inside pocket with at least one upward open space, and a gas generator put in the pocket inside the hood to release oxygen through a chemical reaction for breathing when it is bent inwards to break an inside chemical solution container. However, the hood does not provide a secure seal to the neck for protection against NBC agents.
The ""959 patent to Reisman et al. describes a protective breathing mask comprising a fire-resistant stretchable material shaped as a hood for wearing over and enclosing the head. The hood is primarily designed to combat smoke inhalation and subsequently does not provide suitable filtration or barrier means to NBC agents. Furthermore, exhaled air is trapped within the protective enclosure thereby accumulating moisture and carbon dioxide within the enclosure.
The ""165 patent to Swann describes a deployable hood and mouthpiece having an exhalation check valve to permit exhaled air to flow into the hood. However, the operation of the ""165 patent continually introduces carbon dioxide and moisture into the hood enclosure, thereby fogging up outward visibility and causing the wearer discomfort.
The ""555 patent to Warncke teaches that intermittent exhaled air is used to pressurize a purge zone around the protection zone and is vented to ambient as needed to avoid over-pressurization of said purge zone. No suggestion of any kind is made that such intermittent exhaled air should be admitted into said protection zone. Furthermore, the ""555 patent provides no reservoir of stored pressure during periods of non-exhalation. Accordingly the purge zone in the ""555 patent suffers from a substantial fluctuation in pressure during normal respiration.
The ""861 patent to Warncke teaches that continuously flowing compressed gas from a remote source of compressed gas should flow into a protection zone. No suggestion of any kind is made that said continuous flow of compressed gas should be supplanted by intermittent exhaled air. Similar to the ""555 patent, the ""861 fails to describe a reservoir for pressuring a purge zone absent the remote source of compressed gas.
Consequently, there is a need in the art for an air purifying respirator hood that automatically creates a plenum around the head.
There is a further need in the art to reduce the amount of moisture and carbon dioxide within a hood inflated by the wearer""s exhalation.
There is a further need in the art to increase the overall protection factor of an air purifying respirator hood by providing at least one pressurized zone against the introduction of ambient air into the hood enclosure.
There is a further need in the art to provide a continuously pressurized protective hood without the need for an external air source.
However, in view of the prior art at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.
The above and other objects of the invention are achieved in the embodiments described herein by providing a multiple zone protective enclosure comprising an air-impermeable hood adapted to receive a wearer""s head. The air-impermeable hood has a closed first end and an open second end and an air-impermeable transparent viewing area integrated into the air-impermeable hood, the air-impermeable transparent viewing area adapted to permit outward vision by the wearer. A first substantially airtight seal is provided having a predetermined resistance to airflow, having an outer peripheral edge secured to the second end of the air-impermeable hood, and having an inner peripheral edge adapted to sealingly engage a wearer""s neck. A second substantially airtight seal is provided having a predetermined resistance to airflow, having an outer peripheral edge secured to the second end of the air-impermeable hood and having an inner peripheral edge adapted to sealingly engage a wearer""s neck. The inner peripheral edge of the first substantially airtight seal is adapted to sealingly engage said wearer""s neck along a first annular line of contact and the inner peripheral edge of the second substantially airtight seal is adapted to sealingly engage the wearer""s neck along a second annular line of contact.
The first and second annular lines of contact are disposed in vertically spaced apart relation to one another when the hood encloses the head of the wearer. The air-impermeable hood and the first substantially airtight seal define a protection zone adapted to enclose the head of the wearer. The protection zone is adapted to surround the head of the wearer. A purge zone is defined between the first and second substantially airtight seals and adapted to encircle the neck of the wearer. A respiration interface having an inhalation pathway and an exhalation pathway is provided. The inhalation pathway is adapted to receive purified air and the exhalation pathway adapted to dispatch exhaled air. An exhalation conduit is disposed in fluid communicating relation between the exhalation pathway and the purge zone.
The first and second substantially airtight seals may be constructed in several fashions. In order to conserve production costs, die-cutting may be employed to fabricate the seals. However, in a preferred embodiment, a higher protection factor may be achieved by molding the first substantially airtight seal with a downwardly disposed lip on the inner peripheral edge coming into contact with the wearer""s neck. The downwardly disposed lip increases the surface area of the first substantially airtight seal with the wearer""s neck and also resists the passage of exhaled air into the protection zone.
The exhalation conduit having a one-way check valve means is adapted to restrict the flow of exhaled air only from the exhalation pathway to one or more purge zones. Therefore exhaled air is not directly introduced into the protection zone but is channeled through the exhalation conduit into one or more purge zones.
In the operation of the invention, air exhaled into the exhalation conduit flows into at least one purge zone increasing the air pressure within the purge zone until air, following the path of least resistance, is forced downward and out of the enclosure. During this operation, it is not necessary that the protection zone be pressurized as the purge zone maintains an effective barrier to ambient air outside the hood. This establishes a pressurized zone around the second seal using exhaled air while preventing the exhaled air from accumulating in the protection zone thereby preventing the transparent viewing area from fogging.
In a preferred embodiment of the invention, the exhalation conduit is mated internally within the air-impermeable hood. Alternatively, the exhalation conduit may be mated externally to the air-impermeable hood to discharge exhaled air into one or more purge zones. However, externally mating the exhalation conduit may increase the expense of manufacture and require additional external fittings to the hood that may be exposed to hazardous substances.
Another benefit of internally mating the exhalation conduit is that the first and second substantially airtight seals forming the purge zone into which the exhaled air enters may closely overlay each other. This is achieved by integrating the end of the exhalation conduit from which exhaled air is discharged into the first substantially airtight seal. When the invention is unpressurized, the first and second substantially airtight seals may be in direct contact. However, when exhaled air is discharged between the first and second substantially airtight seals, they are separated by the exhaled air thereby forming the purge zone. Should the conduit be externally mated to the air-impermeable hood, the end of the exhalation conduit from which exhaled air is discharged must be integrated into the side of the air-impermeable hood. This requires the first and second substantially airtight seals to be separated even when in an unpressurized state.
However, in a preferred embodiment, an air-impermeable seal column depends from the second end of the air-impermeable hood. The air-impermeable seal column has a first end and a second end. The first substantially airtight seal is engaged to the second end of the hood and the second substantially airtight seal is engaged to the second end of the seal column thereby vertically spacing the first substantially airtight seal apart from the second substantially airtight seal. This provides a greater comfort level to the wearer, particularly in the neck region as veins and tight-fitting seals that are unevenly distributed may pinch arteries. Another advantage of vertically separating the seals is that the resultant purge zone supports a greater volume of pressurized exhaled air thereby increasing the protection factor of the invention.
A modular purge zone may be prefabricated for integration into the air impermeable hood. The first substantially airtight seal is pre-sealed to the first end of the seal column and the second substantially airtight seal is pre-sealed to the second end of the seal column. Accordingly, a modular purge zone is thereby formed for integration into the air-impermeable hood. Additional modular purge zones may be stacked vertically to provide multiple purge zones.
By varying the relative resistance to airflow between the first and second seals, airflow can be controlled to achieve a desired effect. The variance of airflow resistance may be generally described in three alternative embodiments. In a first embodiment, the first substantially airtight seal has a greater predetermined resistance to airflow than the second substantially airtight seal thereby inhibiting the protection zone from inflating. This embodiment might be preferable in situations where absolutely no fogging of the ocular region is desired for such tasks as sighting a weapon.
In a second embodiment, the first substantially airtight seal has a substantially equal predetermined resistance to airflow than the second substantially airtight seal thereby inhibiting the protection zone from fully inflating.
In a third embodiment, the first substantially airtight seal has a lesser-predetermined resistance to airflow than the second substantially airtight seal thereby fully inflating the protection zone. While the second and third embodiments do introduce a limited amount of carbon dioxide and moisture into the protection zone, they also serve the purpose of heightening the protection factor of the hood by fully or partially pressurizing the protection zone against the introduction of ambient air. Another advantage of pressurizing the protection zone is that the hood expands away from the head of the wearer thereby providing more internal headroom. This is a significant improvement to many existing hoods that are tight fitting and therefore unacceptable to wearers subject to claustrophobia. In one embodiment of the invention, the second substantially airtight seal distal to the first substantially airtight seal encircles the neck of the wearer. In an alternative embodiment, particularly for use in protecting infants and children, the second substantially airtight seal distal to the first substantially airtight seal encircles the torso of the wearer. It is preferable that the seals be constructed of elastomeric material that is resistant to chemical and biological agents such as neoprene, butyl rubber or the like.
It is preferred that elastomeric material having a substantially low elasticity modulus is used to construct the purge zone. Exhaled air flowing into the purge zone causes the purge zone to balloon in volume. This novel feature provides a storage repository for capturing the kinetic energy of the wearer""s exhalation. The ballooning of the purge zone is a combination of increased pressure and increased volume, which is effectively stored as energy potential. The elasticity of the purge zone during periods of non-exhalation (typically during inhalation) contracts the total volume, slowly xe2x80x9cdeflatingxe2x80x9d the balloon. This controlled deflation serves to direct airflow away from the protection zone in a continuous fashion. As exhalations are intermittent, the ballooning effect of this novel invention insures a continuous reservoir of stored pressure. Furthermore, the increase in volume of the purge zone helps equalize variations in the total pressure between wearer inhalation and exhalation. Accordingly, a substantially constant purge zone pressure may be achieved without the introduction of a remote compressed gas source.
As the first and second substantially airtight seals define the purge zone, use of the elastomeric materials having a substantially low elasticity modulus serves another advantage of providing a substantially universal fit. The inner peripheral edge, when formed of elastomeric material, can accommodate a wide range of neck diameters comfortably. This is particularly useful for protecting civilian populations as well as reducing the costs of maintaining a large number of differing sizes in an inventory. Furthermore, because the inner peripheral edge provides the seal, the protective enclosure may be quickly donned without the need of mechanical adjustments.
Still another advantage of using elastomeric material with a substantially low elasticity modulus is that of compacting the enclosure for storage and transport. As opposed to comparatively rigid, face-sealing masks, the air-impermeable hood, transparent viewing area, and airtight seals may all be constructed of substantially flexible air-impermeable material foldable around the respiration interface which is typically a rigid mechanical structure. Face-sealing masks cannot effectively achieve this level of foldability without sacrificing some structural integrity necessary to seal against the face.
Neoprene and butyl rubber are particularly suitable materials for construction of the purge zone. Neoprene is a polymer of the monomer choloroprene, chemical formula CH2:C(Cl)CH:CH2. Neoprene has high resistance to heat and chemicals. Butyl rubber may also be utilized which is prepared by copolymerization of isobutylene with butadiene or isoprene. Butyl rubber is plastic and can be compounded like natural rubber. However, it is difficult to vulcanize. While butyl rubber is not as resilient as natural rubber and other synthetic varieties, it is extremely resistant to oxidation and the action of corrosive chemicals. However, other elastomeric materials with the above-mentioned properties may be suitable as well.
Accordingly, it is an object of the present invention to provide an air purifying respirator hood that automatically creates a plenum around the head.
It is another object of the present invention to reduce the amount of humidity and carbon dioxide within the ocular zone of a hood inflated by the wearer""s exhalation.
It is another object of the present invention to increase the overall protection factor of an air purifying respirator hood by establishing at least one pressurized zone against the introduction of ambient air into the hood enclosure.
It is another object of the present invention to provide a continuously pressurized protective hood without the need for an external air source.
An advantage of the invention is that establishing at least one pressurized zone against the introduction of ambient air into the hood enclosure increases the overall protection factor of the protective hood.
Another advantage of the invention is that exhaled air continually purges the pressurized zones against the introduction of ambient air into the hood enclosure.
Another advantage of the invention is that the hood is continuously pressurized without the need for monitoring the plenum and manually inflating the hood.
Another advantage of the invention is that exhaled air may be used to create a plenum around the head while avoiding the negative effects of carbon dioxide and humidity.
Another advantage of the invention is that the mechanical force required to seal the hood enclosure against the introduction of ambient air is lessened by the pressurized zone that dynamically purge air out of the hood.
Another advantage of the invention is that the protection factor of the protective hood has been greatly increased to permit the use of the hood in applications requiring higher protection against airborne substances than the prior art hoods could provide.
Another advantage of the invention is that the hood is continuously pressurized without the need for an external air source.
These and other important objects, advantages, and features of the invention will become clear as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims.